In a conventional image forming device, such as a laser printer, a process cartridge (process unit) is detachably mounted to a main casing. The process cartridge includes, for example, a drum cartridge and a developing cartridge. The drum cartridge includes a photosensitive drum. The developing cartridge is detachably mounted to the drum cartridge and includes a developing roller that supplies toner to a surface of the photosensitive drum.
In the image forming device provided with the process cartridge, the drum cartridge and the developing cartridge can be integrally detached from and attached to the main casing as an integral process cartridge. Further, only the developing cartridge can be detached from and attached to the main casing with separating the developing cartridge from the drum cartridge, while maintaining the drum cartridge in the main casing.
Further, such a conventional process cartridge is provided with a lock lever. The lock lever prohibits separation of the developing cartridge from the drum cartridge in order to prevent undesired separation. The lock lever is disposed at one widthwise end portion of the drum cartridge. When the developing cartridge is assembled to the drum cartridge, a lower end portion of the lock lever is engaged with a predetermined portion of the developing cartridge from above. When an upper end portion of the lock lever is pressed down, the lower end portion is disengaged from the predetermined portion. Accordingly, the developing cartridge can be separated from the drum cartridge.